Efforts will be focused on x-ray diffraction data collection on single crystals of elongation factor, Tu, complexed with antibiotics. Large crystals of EF-Tu-antibiotic complexes are usually twinned. The twinned crystals can be manually separated but the fragments are generally less than 100 microns in the smallest dimension and poorly diffracting with conventional x-ray sources. Experience has demonstrated that excellent data sets, with resolution extending beyond 2.3 E, can be collected on EF-Tu-antibiotic crystals that are only 20 microns thick. In the next year, efforts will be focused on determining the EF-Tu binding site of three different classes of antibiotics. These include the kirromycin family, the thiazolyl peptide family and the tetracycline family. Ultimately, the identification of antibiotic binding sites will elucidate the mode of action of these antibiotics as well as provide the necessary atomic foundation for the rational design of more effective, less toxic antibiotics.